In order to assure that the peripherals (modems, network
interface cards, NICs, sound cards, video cards, etc.) one can purchase for a modern PC
today will work with virtually any PC, motherboards manufacturers agree to adhere to
several standards in the way the various boards are wired. These standards are called
Architectures.

The surface of a computer motherboard is traversed by thousands of tiny embedded copper
wires which connect everything on the motherboard to everything else. They're much too
small for anyone to determine which architectural model they represent. Instead, the
several types of expansion slots into which one can insert the above-mentioned
peripherals tell us definitively which architectures are represented on the board.

The
first PC IBM designed and marketed in 1981 was called the IBM PC - XT; XT standing for
eXtended Technology. This computer was designed around the Intel 8088 processor which
itself was able to "digest" 8 bits per clock tick. We call the way an XT
computer is wired XT Architecture and the expansion slots one can find on an XT are called
XT slots. By virtue of the 8088 processor being an 8-bit processor, the XT slots are also
8-bit slots -- and any peripheral inserted correctly into an XT slot can also be called an
8-bit peripheral.

When IBM introduced their next PC in 1983, they called it the AT, meaning
"Advanced Technology." This computer was designed around the Intel 080286 chip
-- which was a 16-bit processor. This chip was able to "digest" 16 bits per
clock tick, or two characters, more or less. (see note below) In order for a new
peripheral to send or receive 16 bit per clock into the motherboard on these new '286
computers, designers added a small extension to the XT slot and called the whole black
slot an ISA slot -- Industry Standard Architecture.

With the advent of the '386 processor introduced in 1987 by Intel, the various competing
PC manufactures, IBM, clones, etc, now split ranks and independently designed several
different architectures which competed with each other. IBM developed Micro Channel
Architecture -- or the MCA slot. Not surprisingly, "Big Blue used blue MCA slots on
their '386 computers also called PS2s or Personal System 2 computers. While MCA
architecture is advanced, fast -- at 32 bits per clock tick, IBM asked the clone
manufacturers for a licensing fee in order to use MCA architecture -- and they all
refused. Instead, clone manufacturers decided to design their own architecture around the
Intel '386 chip. A year later, in 1988, one could find EISA slots on these machines. EISA
slots communicated in 32 bit chunks of information with the motherboard bus and started to
show up on clone computers. Unfortunately, motherboard manufacturers discovered that EISA
architecture and their ensuing EISA architecture peripheral cards were much more costly to
produce than an ISA card was. EISA architecture fell out of favor for the general PC
market and can only be found now in server PCs and higher-end PCs.

In 1989, Intel announced the 80486 chip, or the venerable '486. By this time IBM and the
PC clone manufacturers came up with a new architecture which satisfied them all and they
called it VLB or VESA Local Bus. VESA, or Video Electronics Standards Association, is an
acronym, which represents makers of video cards. They were instrumental in designing the
new 32 bit VLB slot -- a simple idea which uses the standard 16-bit ISA slot with another,
shorter 16-bit extension about 3 inches long. Any card which is made to make contact with
all the contacts in the entire VLB slot communicates in 32-bit chunks with the
motherboard.

The Pentium chip debuted in 1993 and allowed for a 32 and 64 bit communication channel
with the motherboard - this new architecture is called PCI or Peripheral Computer
Interface. Designers could had added a 32-bit extension to the VLB slot but this would
have made a PCI card as big as the state of Rhode Island! Instead, a new slot was created
-- the off-white and very stately PCI slot.

Nowadays, modern PC motherboards usually exhibit several ISA slots (which are also XT
slots) and several PCI slots as well. ISA slots will start to disappear on motherboards in
1999 -- they've really outlived their usefulness. When purchasing new card peripherals,
look for a PCI slot version to ensure usability for your subsequent motherboard upgrades.
Enjoy!

Note: Bits per clock ticks have been simplified for ease of explanation. For
those who demand the utmost accuracy, here's the real poop: For example, suppose you're
typing the following on your keyboard -- "The quick brown fox jumped over the lazy
dog's tail."

The reason Pentium chips need only a half clock tick to digest all 64 bits flowing
around a Pentium motherboard is because Pentium chips have two instruction pipelines and
thus can execute 2 instructions per clock cycle. Pentium chips have 2 - 32 bit data
registers - called Superscalar Architecture.